[bgm_co]

I was just using my PC and it just blanked out to a black screen. The PC was running and didn't sound like it was restarting. I tried to turn it off via the power button but this does not respond and the PC keeps running. The only way I can turn the unit off is by cutting the power to the unit, when I plug it back in it automatically starts running but nothing happens and the power button on the front of the PC just doesn't work at all!

The monitor also says there is no input signal whilst the unit is running!

Does anyone have an idea to what is wrong here?

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My first thought here is to check the power supply. It sounds like the voltages are not good on the 3 volt or 5 volt lines causing this. If the power supply tests good then replace the power switch(probably not the problem). The power supply going bad could also have caused the video to go bad from low voltages.

SRX660

[SRX660]

My first thought here is to check the power supply. It sounds like the voltages are not good on the 3 volt or 5 volt lines causing this. If the power supply tests good then replace the power switch(probably not the problem). The power supply going bad could also have caused the video to go bad from low voltages.

SRX660

[bgm_co]

Thank you. What's the best way to test this, how do I identify the 3v and 5v lines?

Would this stop the PC from starting up, when I plug it in it just sounds like it's running. Can't hear any activity from the harddrive trying to load the system up.

[Digerati]

I agree to check the power supply first. Note depending on BIOS setup settings, often a PC will power off if you press and hold the front panel power switch for 4+ seconds.

Here is my canned text on testing PSUs:

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Note the required voltage tolerance ranges:

NOTE: Disregard the -5VDC reading. It is no longer used.

Swapping in a known good supply is a tried and true method of troubleshooting used for years, even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with the known good one, and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

Note the ATX Form Factor standard does not "require" specific color coding for power supply connector wiring. It has recommendations but manufacturers often do not follow them. Sadly, many testing guides or tutorials will refer to wire color only and that can lead to improper testing.

The voltages can be checked in the BIOS Setup Menus of most motherboards but they do not reveal ripple or other anomalies either. And of course, booting into the BIOS Setup Menu requires a working PSU.

As always, before working in the interior of the computer case, take necessary ESD precautions to ensure static buildup in your body does not discharge through and destroy any sensitive devices. Unplug from the wall and touch bare metal of the case before reaching in. And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user-serviceable parts inside a power supply. If you do not have a tester or a suitable spare to swap in, take the PSU to a qualified technician for testing.

[bgm_co]

I don't have anything to test it with, I'll pop to a computer store tomorrow and get a new PSU, hopefully that does the trick!

I'll come back here tomorrow and let you know how I get on.. For now I'll keep it unplugged as it won't turn off any other way..

[Digerati]

Get a good one. Don't feed your computer bad fuel. Here's my canned text on sizing and selecting a PSU.

Use the eXtreme PSU Calculator Lite to determine the minimum and recommended power supply unit (PSU) requirements. Plan ahead and plug in all the hardware you think you might have in 2 or 3 years (extra drives, bigger or 2nd video card, more RAM, etc.). Be sure to read and heed the notes at the bottom of the calculator page. I recommend setting Capacitor Aging to 30% (see my note below), and if you participate in distributive computing projects (e.g. BOINC or Folding@Home) or extreme 3D animated gaming, I recommend setting both TDP and system load to 100%. These steps ensure the supply has adequate head room for stress free (and perhaps quieter) operation, as well as future hardware demands. Research your video card and pay particular attention to the power supply requirements for your card listed on your video card maker's website. If not listed, check a comparable card (same graphics engine and RAM) from a different maker. The key specifications, in order of importance are:

• Current (amperage or amps) on the +12V rail,
• Efficiency,
• Total wattage.

Don’t try to save a few dollars by getting a cheap supply! Digital electronics, including CPUs, RAM, and today's advanced graphics cards, need clean, stable power. A good, well chosen supply will provide years of service and upgrade wiggle room. Look for power supply brands listed under the "Good" column of PC Mech's PSU Reference List. Another excellent read is Tom’s Hardware, Who’s Who In Power supplies: Brands, Labels, And OEMs. Note that some case retailers “toss in” a generic or inadequate PSU just to make the case sale. Be prepared to “toss out” that supply for a good one with sufficient power.

Most PSUs have an efficiency rating of around 70%. This means for every 100 watts of power a PSU draws from the wall, only 70 watts is delivered to the motherboard, with the rest wasted in the form of heat. The best supplies are 85 to 90% efficient, and as expected, cost more. I strongly recommend you pick a quality supply with an efficiency rating equal to or greater than 80%. Look for 80 PLUS and EnergyStar Compliant labels. 80 PLUS PSUs are required to have fairly linear efficiencies. This is important to ensure the PSU is running at or near peak efficiency regardless the load or power demands. Non-linear PSUs typically are most efficient when the load is in a narrow range between 70 and 90% of the PSU’s capacity and the efficiency may drop dramatically above and below those amounts.

Too big of a PSU hurts nothing but your budget. Your computer will draw from the PSU only what it needs, not what the PSU is capable of delivering. If a computer needs 300 watts it will draw 300 watts regardless if the PSU is a 400W, 650W, or 1000W PSU. In turn, the PSU, regardless its size will draw from the wall only what it needs to support the computer. In this example, it will draw 300 watts, plus another 45 – 90 watts, depending on the PSU’s inefficiency.

As noted, the eXtreme Calculator determines minimum and recommended requirements. If the calculator (with the changes I suggested) recommends a 400 watt minimum, a quality 400W supply will serve you just fine. However, a quality 550W – 600W supply will have, among other things, larger heat sinks to dissipate potentially more heat. It might have a larger fan too. The 400W supply will run most of the time closer to capacity, while the larger supply will be loafing along, rarely breaking a sweat. To help the smaller heat sinks get rid of the wasted 80 watts (20% of 400) of heat, the fan in the 400W supply may need to run full speed, while the fan in the larger supply, with bigger sinks just loafs along too – but in near silence. Also, it is typical for manufacturers to use higher quality parts, design, and manufacturing techniques in their higher power supplies.

Note: Capacitor Aging. All electronics “age” over time. Electrons flowing through components bang around and create friction and heat causing wear and tear, altering the electrical characteristics of the device. Over time, this weakens the device resulting in eventual failure. Power supplies have always suffered profoundly from aging effects resulting in a loss of capacity. In recent years, capacitor technologies have improved. The best PSUs use the best (and most expensive) capacitors which suffer less from aging effects than older capacitor types. If planning on buying a new, high-end PSU, setting capacitor aging to 10% may result in a more realistic recommendation. However, headroom “buffer” will be significantly reduced. You can expect your PSU to last 5 years or longer. Since it is better to buy too big rather than too small, and since it is hard to predict what your power requirements will be in 3 years, using 30% for Capacitor Aging ensures you have enough headroom for virtually any upgrade.

Don't forget to budget for a good UPS with AVR (automatic voltage regulation). Surge and spike protectors are inadequate and little more than fancy, expensive extension cords.

[bgm_co]

Ok so I have just bought and installed a new PSU.. And having the same issue. Soon as I turn the mains supply on the system powers up but nothing happens.

*I can still only control the power by the switch on the PSU.
*I still don't get any kind of signal sent to my monitor.
*And it still doesn't sound like the system is starting up.
*All fans are working

Could it be the processor or the motherboard?

[Digerati]

I am sorry to hear that did not resolve your problem. I wish you had a spare or a trusting friend you could swap PSUs with without having to spend money.

Assuming the PSU is connected to the motherboard correctly (both connections) and shorting the two pins on the motherboard does not start the computer, then yes, sadly, it points to the CPU or motherboard. Which one? Can't tell. It would require swapping CPUs to figure that out, or sending the motherboard back to the factory where they have mock-up testing platforms for their motherboards.

There are motherboard testers that can "help" confirm a problem, but they are not conclusive.

Note the switch on the back of the PSU is the master power switch. Not all PSUs have them as they are not required by the ATX Form Factor standard. When on, and the computer is off, the PSU supplies +5Vsb standby voltage to several points on the motherboard for various "wake on..." commands - to allow pressing a key, wiggling the mouse, or pressing the front panel power button to wake it up.

PSUs without the master switch supply the +5Vsb when simply plugged into the wall. In any case, setting the master switch to on, the same as plugging in a non-switched PSU, should NEVER power up and boot the computer.

Outside of verifying all your connections, I am afraid I am at a loss for suggestions. Most users don't have spare CPUs they are willing to sacrifice for testing. If me, I have several laying around, so I might try one - but only one. I would hate to have a bad motherboard take out another CPU, even one I am willing to sacrifice.

[bgm_co]

What do yo mean by shorting the two pins on the motherboard.. Don't think I have tried this yet..

I do have two old PC's, but they are both intel pentium 4's could they be used to test the motherboard?

[bgm_co]

And come to think about it when the computer shut out there may have been a little click I heard... Wound if this could of been something electrical going pop..

The most important thing here is retrieving what's on the harddrives, if the computer has died I guess it's easy replaced.. But like an idiot I haven't backed my work up since May.

[SRX660]

The processor only does one thing. It routes data to all the hardware in the computer. It is probably working fine. The next thing to check is the power switch. You can use a multimeter to test it. NOW, the power switch is a momentary switch. What that means is that it really only sends a signal to the motherboard to start up. Just a quick voltage to the chipsets starts the bootup process and then there is no more voltage that goes thru the switch. Test the switch usually takes 2 people unless you have a shop setup like i do with vise type holders to hold various hardware so i can work on or test them. Holding the multimeter pins in the socket that plugs into the motherboard, watch the meter while someone clicks the switch, to see if you get a voltage spike on the meter. If so then the switch is good but if not then replace the switch. If you have a reset button on your computer you might try switching it over to the power plug pins and see if that fixes the problem.

Most computers make some kind of sound when the BIOS boots up telling you all the hardware is working. After the hardware check the bios looks for the boot ini file(always in a certain place on the HD) to tell the computer what to do next. The boot ini tells it to read the files that starts windows.

You are at the point where it may(or not)boot into windows but you just cant see it(no graphics).A check here to see if the graphics (display)is working is to hold the delete key down while the computer is booting. This varies for different computers (may be the F1, F2, F8 or even the esc key on some computers)but doing this should get you to a blue BIOS screen. If you cannot even get to a BIOS screen either the on-board video or the video card has gone bad. Replacing the motherboard(with on-board video) or the video card should fix this problem.Replacing the power switch may fix some problems(shutoff).

Below are tools i made from old computer parts to test switches.

The bottom tool is nothing more that a fan plug off a power adapter.




Most motherboards have lettering on the power strip. Do you see where it says PW and RES. These are the power and reset switch pins.


By using a simple tester i can find out if a switch is bad quickly. OL on the tester means a open connection. When i hit the switch it jumps up to 1.100 which tells me the switch is working.


If i knew what your computer is i could tell you the next step in the process.If you can get to the BIOS screen and the switch tests good, i would suspect a bad motherboard.

SRX660

[bgm_co]

Thank you, I will try all that tonight and let you know how I get on..

[Digerati]

What do yo mean by shorting the two pins on the motherboard.. Don't think I have tried this yet..

The motherboard has a "front panel I/O header" of about 16 pins. In this header, you connect the HD LED wires, Reset switch wires, the PWR_On LED, perhaps a case speaker (if not on-board), but also, the Power Switch's pair of wires.

The front panel power switch simply shorts those two pins together which signals the PSU to start up. When the motherboard is out of the case, or to by-pass and test the front panel power switch, you can (CAREFULLY) short those two pins with a small screw driver or the like to start the PSU and boot process. Not only be super careful sticking a hardened steel screwdriver in there, but touch bare metal of the case to discharge static from your body first.

As noted, this is a "momentary" circuit (not button). You can press and hold the button and maintain the short. But the circuit is intelligent, and ignores the button once the short if detected - at least for awhile. So, with your screwdriver, get in, short and get out so you don't accidentally touch something else.

Alternatively, if you will be doing maintenance often, getting a remote switch (like the blue & white wired switch in the image above) or this to connect to the motherboard in place of the case switch is handy, and avoids sticking metal objects into live electronics.

The processor only does one thing. It routes data to all the hardware in the computer. It is probably working fine

Ummm, routing data is really the operating system's job. The CPU just crunches numbers, and only when instructed too. It is pretty dumb, otherwise.

At this point, with the described symptoms of the the system not turning on, fans working, I am not ready to rule out the CPU as the cause. A bad CPU will prevent you from accessing the BIOS Setup Menu too.

You have not mentioned any beeps. Does your motherboard have an integrated system speaker? If not, you will need to connect the case speaker to that same front panel header. If no case speaker and your motherboard does not have one mounted, you might order one of them too (see here).

As SRX660, suggested, if we knew your hardware specs, we could probably be more specific.

[Digerati]

I forgot - as far as the click - clicks don't scare me. "Pops" do. You might jam your nose in there and take a big whiff. You should not smell anything burnt.

[bgm_co]

Most computers make some kind of sound when the BIOS boots up telling you all the hardware is working. After the hardware check the bios looks for the boot ini file(always in a certain place on the HD) to tell the computer what to do next. The boot ini tells it to read the files that starts windows.

I'm sure it use to beep when started up.. But doesn't now.

I have tried shorting the power pins for the on off switch no joy. :-(